1. Field of the Invention
The present invention relates to the field of plant breeding and variety development, and more specifically, relates to the development of a new and distinct broccoli type for easier harvest.
2. Description of Related Art
Broccoli is a native of the Mediterranean region, and has been grown in Italy from at least the time of the Roman Empire. It was a favorite vegetable in Rome where a variety called Calabrese was developed. Before the Calabrese variety was cultivated, Romans ate a purple sprouting broccoli that turned green when cooked.
During the 16th century, the popularity of broccoli spread throughout Europe and it was cultivated in the United States by the late 18th century. However, broccoli did not become a commercially important crop in the United States until after World War II. In the late 20th century broccoli became popular in the United States, and has recently been touted for its health benefits. Presently, the United States is the world's largest producer of broccoli, with most of the broccoli grown in the U.S. marketed as fresh produce. The leading broccoli-producing states are California (with approximately 90 percent of the crop), Arizona, Texas, and Oregon. Broccoli also is grown on a large scale in Spain, northern Europe, Central America and Australia.
Broccoli is a member of the Cruciferae family, as are cabbage, cauliflower, brussels sprouts, kohlrabi, turnips, mustards, and Chinese cabbage. The word broccoli comes from the Italian word “brocco”, which means arm branch, more particularly, from the word broccolo, which is the diminutive form of brocco and refers to cabbage sprout. Broccoli is plural and refers to the numerous shoots in this form of Brassica oleracea. 
There are several types of broccoli, the most popular being the sprouting/Italian broccoli that includes the Calabrese-type, Brassica oleracea L. convar. botrytis (L.) Alef. var. cymosa Duch. (the name adopted by the Community Plant Variety Office (CPVO)). Heading broccoli has several attributes more commonly attributed to cauliflower (an example being the Romanesco type, which is increasing in popularity). The true Calabrese type is a primitive type with many secondary heads (origination from the axils of the leaves). The heads are also split into smaller parts, that do not form a solid head.
Another broccoli, “broccoli rabe”, or, “broccoli raab” has loose green sprouting heads (more like loose broccoli than cauliflower) that are harvested and eaten as greens along with surrounding leaves.
Morphologically, cauliflower and heading broccoli are similar. The broccoli plant, however, generally produces a green head with a longer and more slender floret-stalk than cauliflower. When the main terminal head of a broccoli plant is harvested, the axillary buds lower on the main stem are induced to develop into smaller heads, which can also be harvested.
Much of the breeding of modern varieties has focused on heading types, which have been bred to produce a single, large head at the plant axis, reducing the number of secondary heads, though in some regions after the harvest of the main head secondary heads are still harvested, sometimes referred to as “asparagus broccoli”.
The most commonly grown broccoli variety is Marathon, which shows average to good vigor, with the height of the head at about 40-50 cm above the ground, and the height of the canopy at about 60-70 cm. Maturity is medium to late (70 days in the summer from planting), with secondary heads present. The color of the head is grey/green, with the head forming a medium dome in shape. The bead on the heads is fine, the stem diameter is medium, somewhat sensitive to hollow stem, and the variety has intermediate resistance to downey mildew (Peronospora parasitica). Marathon is best adapted to cool season cultivation, (fall, winter) and the plant density varieties between 40,000 to 80,000 plants per ha.
Most broccoli varieties grow best on well-drained soils that hold water. In sandy soils, irrigation is important for optimum plant growth and to maintain proper main head and side shoot development. Flower heads (the edible portion of sprouting broccoli) develop relative to ambient temperatures, and in the heat of summer, broccoli heads maturing in July may produce flowers and seeds more quickly (four to six days) than those maturing in the cooler spring and fall periods.
To be considered good quality, broccoli heads should be closed, dark green and tight (no yellow petals showing). A deep green, uniform head color is a desirable trait in broccoli. Broccoli heads “green” according to the amount of sunshine reaching the crown of the heads, the crown being the upper surface of the broccoli head covered by the florets. The present commercial heading broccoli varieties all have a high canopy that shades at least portions of the head, particularly at the margin of the crown, resulting in yellowing around the outer extremities of the harvested broccoli heads, sometimes even causing extensive yellowing of individual florets at the center of the crown.
Broccoli is typically planted in the range of 30,000 to 40,000 plants per hectare, though in North America it is common to plant broccoli at a higher density, of 40,000 to as high 100,000 plants per hectare. At higher densities, the broccoli plants will produce smaller heads. In common with other cole crops, broccoli can be established in the field by direct-seeding or by transplanting. Many factors, such as soil type, organic matter content and soil moisture interact to influence germination and emergence. A more uniform, as well as earlier, broccoli crop can be grown from transplants raised in plugs or flats in a greenhouse. Such transplants can be planted in the field during late April, although the plants must be hardened off before being set out.
The edible portion of broccoli is the unopened flowering heads. Broccoli heads are susceptible to a number of defects that may relate to climatic or growth aberrations, though some appear to be cultivar related. Many defects can be avoided by harvesting at the correct stage so that the heads do not become overmature. A post-mature crop will show advanced flower development, with yellowing of the heads. Overmature plants also commonly developing fibrous stems.
Harvesting at the correct stage and proper handling afterwards are very important with broccoli, as it is a perishable commodity. For this reason, uniformity of maturity and concentrated harvesting have been the most highly desirable characteristics in broccoli varieties.
Harvested broccoli is often cooled with packed ice or a hydro-cooler immediately after harvest. Broccoli that is cooled and maintained at 32° F. and 95 to 100 percent relative humidity can be stored for 10 to 14 days. If broccoli is stored this long, however, it will begin to lose its dark green color and firmness, affecting its marketability.
Since harvesting is the single most expensive cultural operation, it is imperative that these costs be kept to a minimum. The present trend is to harvest only the main terminal heads, usually by hand. Certain mechanical harvest aids are used, but complete mechanical harvesting has not been adopted. Use of modern, more uniform hybrids has enabled growers to complete harvesting in two or, at the most, three manual cuts through the field.
In a study reviewing harvest practices from 1985-1990 in the United States, the time required for cutting broccoli was reported to be on the order of 60 man-hours/ha. Overall costs for cut/pack/haul/cool and sell was reported as $2125/ha, with the cost of the cut alone being $500/ha. The labor requirements for harvesting are well over 50% of the total labor costs for growing broccoli.
Converting from hand to machine harvesting of broccoli could reduce these labor requirements by a great deal. However, in testing different cultivars, transplant times, growing techniques and harvest methods, a recent study determined that once over mechanical harvest of broccoli inflorescences, or heads, compared to the graduated traditional hand-harvest (picking repeatedly 6 to 8 times), results in a yield reduction on the order of 49% to 60%, depending on the variety. A combination of hand harvest for the primary heads, followed by a mechanical picking of the secondary heads was proposed as reducing yield losses, though still on the order of about 23% (Dellacecca, V. 1996, New agrotechniques to promote broccoli picking. Acta Hort. (ISHS) 407:347-352).
There have been efforts aimed at the improvement of broccoli to produce varieties better suited to mechanized harvesting. One factor limiting the performance of a mechanical harvester is the phenotypic appearance of the broccoli varieties and a lack of uniformity in maturity (Casada, J. H.; Walton, L. R.; Bader, M. J. (1988) Single pass harvesting of broccoli, Am Soc Agr Eng Microfiche Collect. (fiche # 88-1041) p. 11; Bon, T. A. (1997) Senior design project development of a non-selective broccoli harvester, American Society of Agricultural Engineers No. 97-1018, pp 17). Generally, there is wider acceptable maturity range for processing broccoli compared with fresh market broccoli, which requires a more uniform product (Shearer, S. A.; Jones, P. T.; Casada, J. H.; Swetnam, L. D. (1991). A cut-off saw mechanism for selective harvest of broccoli. Transactions of the American Society of Agricultural Engineers 34 (4): 1623-1628.)
Thus, the selection of appropriate broccoli plant types for uniformity of maturity has been identified as one factor in the success of any broccoli harvester project (Bon, T. A., 1997). Harvesting of broccoli, either by hand or machine, could also be facilitated by an elongated growth habit that results in the protrusion, or exsertion, of the head above the general level of the broccoli foliage (Baggett, J. R., Kean, D., & Kasimor, K. (1995). Inheritance of internode length and its relation to head exsertion and head size in broccoli, J. Am. Society of Hort Sci. 120 (2): 292-296).
Another issue is that in harvesting broccoli leaves attached to the severed head must be removed manually. Accomplishing this task mechanically presents a further obstacle in the development of full mechanisation of harvest. (Casada .J. H., Shearer, S. A. and P. T. Jones (1991) Development of a mechanized selective harvester for cole crops, Am Soc of Agr Engineers. Albuquerque, N. Mex., Jun. 23-26, 1991, Paper # 91-1018, p 17). In this regard, incorporating mechanical defoliation of the broccoli plants into a harvester design is an area undergoing investigation, in the hope that successful implementation of a defoliation operation into a harvester would improve the overall efficiency of the harvest and packing (Bon, T .A., 1997).
The successful development of mechanized harvest would greatly improve the overall efficiency of the harvest and packing (Bon, T. A., 1997). However, attempts to develop a broccoli harvester have not been successful with present day broccoli plant types, due in part to the many simultaneous problems that must be overcome in adapting broccoli varieties for mechanization. In one article this problem is presented as requiring the selection of varieties with their heads well above the ground, with a more open leaf posture, and with leaves that are well separated from (or uncover) the bottom of the head. (Chou broccoli:La recolte mecanique devient possible. A&D, 07/2001 #68. Also in UNILET informations, #107-Janvier 2001). To date, the development of a broccoli plant type simultaneously providing these multiple solutions in a commercially acceptable context has presented an insurmountable problem for the breeding community.